linux-kernel - Re: [PATCH 2/2] can: add Transmitter Delay Compensation (TDC) documentation

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Message-ID: <aOzJZ1NsKxNMvIzJ@horms.kernel.org>
Date: Mon, 13 Oct 2025 10:41:59 +0100
From: Simon Horman <horms@...nel.org>
To: Vincent Mailhol <mailhol@...nel.org>
Cc: Oliver Hartkopp <socketcan@...tkopp.net>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-can@...r.kernel.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] can: add Transmitter Delay Compensation (TDC)
 documentation

On Sun, Oct 12, 2025 at 08:23:43PM +0900, Vincent Mailhol wrote:

...

> @@ -1464,6 +1464,66 @@ Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
>     can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
>  
>  
> +Transmitter Delay Compensation
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +At high bit rates, the propagation delay from the TX pin to the RX pin of
> +the transceiver might become greater than the actual bit time causing
> +measurement errors: the RX pin would still be measuring the previous bit.
> +
> +The Transmitter Delay Compensation (thereafter, TDC) resolves this problem
> +by introducing a Secondary Sample Point (SSP) equal to the distance, in
> +minimum time quantum, from the start of the bit time on the TX pin to the
> +actual measurement on the RX pin. The SSP is calculated as the sum of two
> +configurable values: the TDC Value (TDCV) and the TDC offset (TDCO).
> +
> +TDC, if supported by the device, can be configured together with CAN-FD
> +using the ip tool's "tdc-mode" argument as follow::
> +
> +- **omitted**: when no "tdc-mode" option is provided, the kernel will

Hi Vincent,

I'm unsure why, but make htmldocs reports:

.../can.rst:1484: ERROR: Unexpected indentation. [docutils]

> +  automatically decide whether TDC should be turned on, in which case it
> +  will calculate a default TDCO and use the TDCV as measured by the
> +  device. This is the recommended method to use TDC.

...